WU Wenjun, HAN Zhao, ZHANG Fuyuan, LIU Pengfei, LI Jie
(School of Metallurgical Engineering, Anhui University of Technology, Ma’anshan 243000, China)
Abstract
Objective Various application areas put forward demanding requirements for high-purity iron oxide nanoparticles with high purity,small particle size and narrow particle size distribution. Currently, studies on prepared iron oxide nanoparticles pay less attentionto the purity, mainly because of the failure to purify the iron source used in the experiments. It is difficult to completely removethe remaining ammonium ion and sulfate ion in the iron oxide by hydrothermal method of preparation, so there is a need to find anoperationally simple and effective method for the preparation of high-purity iron oxide nanoparticles. To prepare high-purity ironoxide nanoparticles, the preparation method of iron oxide nanoparticles needs to be further improve, followed by detailed phaseanalysis.
Methods Firstly, the recrystallization method was used to purify ferrous sulfate at one time. The saturated ferrous sulfate solution was put into a low-temperature circulating thermostat for crystallization, and the ferrous sulfate crystals were prepared after removing impurities. The crystallization processes above were repeated until the purity reached the requirements. Secondly, the second purification of ferrous sulfate was carried out by ammonium fluoride precipitation method. The ferrous sulfate crystals afterthe initial purification were first configured as a solution, and then ammonium fluoride and ammonia were added to the ferroussulfate solution. After precipitation and removing the impurities, a pure ferrous sulfate solution was obtained. Finally, hydrogen peroxide was added to the pure ferrous sulfate solution for oxidation. The hydroxyl iron oxide was precipitated by adding ammonia.After further removing impurities by the slurry mixing method and ultrasonic washing method, the iron oxide precursor was prepared and calcined to obtain high-purity nano iron oxide. Subsequently, atomic absorption spectroscopy and inductively coupled plasma atomic emission spectrometry were used to analyze the ionic mass concentration in ferrous sulfate solution and high-purity nano iron oxide. An X-ray diffractometer was used to analyze the phase composition, field emission scanning electron microscopywas used to analyze the particle morphology and a nanolaser particle size analyzer was used to analyze the particle size distributionof the final product of high-purity nano iron oxide.
Results and Discussion When the ferrous sulfate solution is purified by recrystallization method, the crystallization temperature ofthe saturated ferrous sulfate solution is selected as 10 ℃, and the mass concentrations of impurities Ca2+, Mg2+ and Mn2+ in ferrous sulfate decrease from 161, 128 and 91 mg / L to 20, 16 and 6 mg / L respectively. With the increase of ferrous sulfate solution pH, the mass concentration of Ca2+, Mg2+ impurities decreases, Ca2+, Mg2+ impurities form CaF2, MgF2 precipitates. When the pH is 6, the mass concentration of Ca2+, Mg2+ in the ferrous sulfate solution is 11.5, 7.0 mg /L, and when the pH is more than 7, more FeOOH precipitates are generated in the solution. When the solution pH is 4, there is a minimum point in the removal of Ca2+ and Mg2+ because [MFn ] 2-n coordination ions (M is impurity ions such as Ca2+ and Mg2+) are formed when the solution pH is from 3. 5 to 4, and part of the CaF2 and MgF2 precipitates will be re-dissolved, which leads to a slowdown in the trend of decreasing the mass concentration of Ca2+ and Mg2+ in the solution. Therefore, the pH of ferrous sulfate solution is adjusted to 6 with dilute ammonia water when the ferrous sulfate solution is purified by the ammonium fluoride method, the reactiontemperature is set to 30 ℃ , the excess coefficient of ammonium fluoride is set to 5, and the mass concentrations of Ca2+ and Mg2+ in the ferrous sulfate solution are reduced to 10. 4 and 6. 5 mg / L respectively. The concentration of ammonium ion and sulfate ion in the filtrate decreases from 3, 500 mg / L to 18 mg / L after 8 times of slurry washing and 17 mg / L after 3 times of ultrasonic washing, which tends to be stable. The SEM image results show that at the roasting temperature of 600 ℃ , the high-purity ironoxide nanoparticles are all spherical particles with uniform morphology and nanometer size, and there are agglomerates betweenthe particles, which is because high-purity iron oxide nanoparticles have a small diameter, large specific surface area, high surface energy, and easy to produce agglomerates. The results of the particle size distribution show that the median particle size D50 of iron oxide is 300 nm, and the particle size distribution is narrow.
Conclusion The XRD pattern result indicates that the product calcined at from 600 ℃ to 800 ℃ shows better crystallinity. At the calcined temperature of 600 ℃ , the high-purity iron oxide nanoparticles are all spherical particles with uniform morphology andnanometer size, and there are agglomerations between the particles. The prepared high-purity nano iron oxide is sphericalparticles, with uniform morphology, a median particle size of 300 nm, and the mass fraction of α-Fe2O3 in high-purity nano-iron oxide is greater than 99. 95%.
Keywords: high purity nano iron oxide; recrystallization method; ammonium fluoride precipitation; mixing-ultrasonic washing method; ammonia precipitation; phase analysis
Get Citation：WU W J, HAN Z, ZHANG F Y, et al. Preparation of high-purity nano iron oxide[J]. China Powder Science and Technology, 2024, 30(1): 56-65.
Received: 2023-07-07,Revised:2023-11-16,Online:2023-11-28。
Funding Project:国家自然科学基金项目 ,编号:52074003。
First Author:吴文军 (1999—) ,男,硕士生 ,研究方向为粉体制备技术。 E-mail: w543150801@163.com。
Corresponding Author:韩召 (1976—),男,副教授 ,博士 ,硕士生导师 ,研究方向为粉体制备及应用技术。 E-mail: authan@163.com。
DOI:10.13732 / j.issn.1008-5548.2024.01.006
CLC No : TQ138. 1; TB4 Type Code :A
Serial No:1008-5548(2024)01-0056-10
